T5 model support

[havietisov]

Any plans on adding T5 models?
FLAN-T5 are particularly interesting

[shermansiu]

Yes. See #187. It's also on the dev roadmap (#244).

[nlpkiddo-2001]

Any updates reg this?

[shermansiu]

In #187 (comment), js8544 mentioned that his team would be working on it in November, but no updates have come since then.

[hmellor]

Closing as duplicate of #187